In a mobile terminal device such as a cellular phone and PDA, to prevent a shock and external force from being applied to the display, a protective plate made of plastic, for example, protective plate made of acrylic resin with high transparency is disposed at a predetermined distance outside the display (for example, Patent Document 1).
However, since the protective plate made of acrylic resin tends to bend by external force, it is necessary to set the distance between the protective plate and display at a large extent to which the bending can be absorbed. Further, it is required to increase the thickness to provide the protective plate made of acrylic resin with strength to some extent. Therefore, it has become difficult to actualize thinner mobile terminal devices.
Then, to actualize thinner mobile terminal devices, proposed is a protective plate using chemically strengthened glass which suppress bending and is a thin plate while having strength (for example, Patent Document 2). Patent Document 2 describes cover glass for mobile terminals obtained by cutting plate glass of a specific glass composition into a predetermined shape, chamfering the edge face, performing mirror polishing processing on both surfaces, and then forming a compressive stress layer in the surface by chemical strengthening, thereby suppressing its bending and reducing its tendency to break, and a manufacturing method of the cover glass.    Patent Document 1: Japanese Unexamined Patent Publication No. 2004-299199    Patent Document 2: Japanese Unexamined Patent Publication No. 2007-99557